This application claims the benefit of Korean Patent Application No. 2000-45636, filed on Aug. 7, 2000, which is hereby incorporated by reference as if fully set forth herein.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device implementing in-plane switching (IPS) where an electric field to be applied to liquid crystal is generated in a plane parallel to a substrate.
2. Discussion of the Related Art
A liquid crystal display device uses the optical anisotropy and polarization properties of liquid crystal molecules to produce an image. Liquid crystal molecules have a definite orientational alignment as a result of their long, thin shapes. That orientational alignment can be controlled by an applied electric field. In other words, as an applied electric field changes, so does the alignment of the liquid crystal molecules. Due to the optical anisotropy, the refraction of incident light depends on the orientational alignment of the liquid crystal molecules. Thus, by properly controlling an applied electric field a desired light image can be produced.
While various types of liquid crystal display devices are known, active matrix LCDs having thin film transistors and pixel electrodes arranged in a matrix are probably the most common. This is because such active matrix LCDs can produce high quality images at reasonable cost.
Recently, liquid crystal display (LCD) devices that are light and thin and have low power consumption characteristics are used in office automation equipment and video units and the like. Driving methods for such LCDs typically include a twisted nematic (TN) mode and a super twisted nematic (STN) mode. Although TN-LCDs and STN-LCDs have been put to practical use, they have a drawback in that they have a very narrow viewing angle. In order to solve the problem of narrow viewing angle, in-plane switching liquid crystal display (IPS-LCD) devices have been proposed. The IPS-LCD devices typically include a lower substrate where a pixel electrode and a common electrode are disposed, an upper substrate having no electrode, and a liquid crystal interposed between the upper and lower substrates.
A detailed explanation about operation modes of a typical IPS-LCD panel will be provided referring to FIGS. 1 to 3.
As shown in FIG. 1, upper and lower substrates 1 and 2 are spaced apart from each other, and a liquid crystal layer 3 is interposed therebetween. The upper and lower substrates 1 and 2 are called color filter substrate and array substrate, respectively. Pixel and common electrodes 4 and 5 are disposed on the lower substrate 2. The pixel and common electrodes 4 and 5 are parallel with and spaced apart from each other. The pixel and common electrodes 4 and 5 apply a horizontal electric field 6 to the liquid crystal layer 3. The liquid crystal layer 3 has a negative or positive dielectric anisotropy, and thus it is aligned parallel with or perpendicular to the horizontal electric field 6.
FIGS. 2A and 2B conceptually illustrate operation modes of a conventional IPS-LCD device. When there is no electric field between the pixel and common electrodes 4 and 5, as shown in FIG. 2A, the long axes of the liquid crystal molecules maintain an angle from a line perpendicular to the parallel pixel and common electrodes 4 and 5. Herein, the angle is 45 degrees, for example.
On the contrary, when there is an electric field between the pixel and common electrodes 4 and 5, as shown FIG. 2B, there is an in-plane horizontal electric field 6 parallel with the surface of the lower substrate 2 between the pixel and common electrodes 4 and 5. The in-plane horizontal electric field 6 is parallel with the surface of the lower substrate 2 because the pixel and common electrodes 4 and 5 are formed on the lower substrate 2. Accordingly, the liquid crystal molecules are twisted so as to align, for example, the long axes thereof with the direction of the horizontal electric field 6, thereby the liquid crystal molecules are aligned such that the long axes thereof are parallel with the line perpendicular to the pixel and common electrodes 4 and 5.
By the above-mentioned operation modes and with additional parts such as polarizers and alignment layers, the IPS-LCD device displays images. The IPS-LCD device has wide viewing angles since the pixel and common electrodes are together placed on the lower substrate. Moreover, the fabricating processes of this IPS-LCD device are simpler than those of other various LCD devices.
However in the IPS-LCD device, a color-shift which depends on the viewing angle still remains. It is already known that this color-shift is not acceptable for full color-image display. This color-shift is related to a rotational direction of the liquid crystal molecules under application of electric field when the applied voltage is greater than a threshold voltage. Moreover this color-shift is caused by increasing or decreasing of an optical retardation xcex94n d of the liquid crystal layer with viewing angle.
For the sake of discussing the above-mentioned problem of the IPS-LCD device, with reference to FIG. 3, a specific pixel structure of the IPS-LCD device is used and will be described in detail.
As shown in FIG. 3, the pixel and common electrodes have bend angle xcex1. This bent electrode structure permits rotation of the liquid crystal molecules 9 in opposite directions in each pixel when voltage is supplied to the bent electrodes. Therefore, the bent electrodes and the oppositely directed liquid crystal molecules divide the pixel into two different regions with different viewing angle characteristics. And thus, the color-shift can be effectively compensated by this multi domain structure.
However, since the IPS-LCD device has the above-mentioned bent electrodes, the liquid crystal molecules around the bend portions of the bent electrodes are not properly rotated, i.e, an abnormal arrangement, when the voltage is supplied to the electrodes. Namely, the liquid crystal molecules, which are arranged parallel with the horizontal electric field when the voltage is applied, are disordered in the boundary between two domains because of these bent electrodes. Therefore, light cannot appropriately pass through this portion of the liquid crystal layer, and thus the brightness is lowered.
Accordingly, the present invention is directed to an IPS-LCD device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an array substrate for use in an IPS-LCD device which depresses a color-shift.
Another object of the present invention is to provide an array substrate for use in an IPS-LCD device which prevents a deterioration of the brightness.
In order to achieve the above object, the first preferred embodiment of the present invention provides an array substrate for use in an in-plane switching liquid crystal display device including a gate line on a substrate; a data line over the substrate, the data line being perpendicular to the gate line; a common line on the substrate, the common line being parallel with and spaced apart from the gate line; a plurality of common electrodes extended from the common line, wherein each common electrode has a plurality of bend portions, and wherein each inner part of the bend portions is filled with a conductive material; a plurality of pixel electrodes spaced apart from the common electrodes, wherein each pixel electrode has a plurality of bend portions and corresponds to each common electrode; and a switching element electrically connected to the gate and data lines, the switching element supplying voltage to the pixel electrodes.
The present invention also provides, in another aspect, an array substrate for use in an in-plane switching liquid crystal display device including a gate line on a substrate; a data line over the substrate, the data line being perpendicular to the gate line; a common line on the substrate, the common line being parallel with and spaced apart from the gate line; a plurality of common electrodes extended from the common line, wherein each common electrode has a plurality of bend portions; a plurality of pixel electrodes spaced apart from the common electrodes, wherein each pixel electrode has a plurality of bend portions and corresponds to each common electrode, and wherein each inner part of the bend portions is filled with a conductive material; and a switching element electrically connected to the gate and data lines, the switching element supplying voltage to the pixel electrodes.
The present invention also provides, in another aspect, an array substrate for use in an in-plane switching liquid crystal display device including a gate line on a substrate; a data line over the substrate, the data line being perpendicular to the gate line; a common line on the substrate, the common line being parallel with and spaced apart from the gate line; a plurality of common electrodes extended from the common line, wherein each common electrode has a plurality of bend portions, and wherein each inner part of the bend portions is filled with a conductive material; a plurality of pixel electrodes spaced apart from the common electrodes, wherein each pixel electrode has a plurality of bend portions and corresponds to each common electrode, and wherein each inner part of the bend portions is filled with a conductive material; and a switching element electrically connected to the gate and data lines, the switching element supplying voltage to the pixel electrodes.
A side of each common electrode forms an angle xcex2 with a line extended from a side of the inner part of the bend portion, wherein the side of the each common electrode forms an angle {circle around (-)} with a vertical line that is parallel with the data line, wherein the angle xcex2 is greater than 0xc2x0, and wherein the angle xcex2 is less than or equal to the angle {circle around (-)}.
A side of each pixel electrode forms an angle xcex2 with a line extended from a side of the inner part of the bend portion, wherein the side of the each pixel electrode forms an angle {circle around (-)} with a vertical line that is parallel with the data line, wherein the angle xcex2 is greater than 0xc2x0, and wherein the angle xcex2 is less than or equal to the angle {circle around (-)}.
The present invention also provides, in another aspect, an array substrate for use in an in-plane switching liquid crystal display device including a gate line on a substrate; a data line over the substrate, the data line being perpendicular to the gate line; a common line on the substrate, the common line being parallel with and spaced apart from the gate line; a plurality of common electrodes extended from the common line, wherein each common electrode has a plurality of bend portions, and wherein each inner part of the bend portions has a round shape; a plurality of pixel electrodes spaced apart from the common electrodes, wherein each pixel electrode has a plurality of bend portions and corresponds to each common electrode; and a switching element electrically connected to the gate and data lines, the switching element supplying voltage to the pixel electrodes.
The present invention also provides, in another aspect, an array substrate for use in an in-plane switching liquid crystal display device including a gate line on a substrate; a data line over the substrate, the data line being perpendicular to the gate line; a common line on the substrate, the common line being parallel with and spaced apart from the gate line; a plurality of common electrodes extended from the common line, wherein each common electrode has a plurality of bend portions, and wherein each inner part of the bend portions has a round shape; a plurality of pixel electrodes spaced apart from the common electrodes, wherein each pixel electrode has a plurality of bend portions and corresponds to each common electrode; and a switching element electrically connected to the gate and data lines, the switching element supplying voltage to the pixel electrodes.
The present invention also provides, in another aspect, an array substrate for use in an in-plane switching liquid crystal display device including a gate line on a substrate; a data line over the substrate, the data line being perpendicular to the gate line; a common line on the substrate, the common line being parallel with and spaced apart from the gate line; a plurality of common electrodes extended from the common line, wherein each common electrode has a plurality of bend portions, and wherein each inner part of the bend portions has a round shape; a plurality of pixel electrodes spaced apart from the common electrodes, wherein each pixel electrode has a plurality of bend portions and corresponds to each common electrode, and wherein each inner part of the bend portions has a round shape; and a switching element electrically connected to the gate and data lines, the switching element supplying voltage to the pixel electrodes.
The round shape of each bend portion satisfies a condition defined by a diameter of a circle that is abutted on an arc of the said round shape.
The diameter beneficially ranges from 7 xcexcm to 170 xcexcm.
The diameter also ranges from 30 xcexcm to 170 xcexcm.
The diameter also ranges from 70 xcexcm to 100 xcexcm.
Each outer part of the bend portions of the said common electrodes has a round shape, and each outer part of the bend portions of the said pixel electrodes also has a round shape.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.